Piano sound board



April 4, 1967 H. K. GRAVES PIANO SOUND BOARD Filed Oct. 22; 1965 HOWARDK. GRAVES INVENTOR.

United States Patent 6 3,312,136 PIANO SOUND BOARD Howard K. Graves,6633 Somerset Drive, Cleveland, Ghio 44141 Filed Get. 22, 1965, Ser. No.501,661 8 Claims. ((Il. 84-492) This invention relates to sound boardsfor stringed musical instruments, and more particularly relates to animproved sound board for pianos.

The sound board of a piano radiates into the air the sound energy of thevibrating strings. The sound board serves as an acoustical couplingbetween the strings and the air. The sound board is driven by thestrings through a bridge that forms one of the vibrational ends of thestrings.

The vibrating strings must be supported at the bridge by a proper degreeof acoustical stiffness. This acoustical stiffness regulates the rate atwhich energy is transferred from the vibrating strings to the air. Eachstring must be supported at the bridge with a proper degree ofacoustical stiffness for the tone to be pleasing. If the degree ofstiffness is not sufficient, the energy of the string will betransferred to the air too rapidly and the tone will sound like a dullthud. If the degree of stiffness is excessive, the energy of the stringwill not be transferred rapidly enough and the tone will be thin. Theproper degreeof stiffness is a function of both the frequency of thestring and the tension of the string. Higher pitched strings requiremore stiffness than lower pitched strings, and higher tensioned stringsrequire more stiffness than lower tensioned strings.

The sound board of a conventional piano performs two functions: itradiates sound and it supports the strings. The conventional sound boardis a wooden, structural diaphragm that is secured to the frame or caseof the instrument. 7 The required acoustical stiffness at the bridge isprovided by the structural plate rigidity of the diaphragm. The soundboard radiates sound energy into the air by vibrating diaphragmaticallywith the bridge as a driving point.

The requirements that the sound board both radiate sound and provide astiff support for the strings are mutually conflicting. A sound boardthat i sufficiently stiff to support the strings with the requireddegree of acoustical stiffness is not sufficiently light and free to beable to respond to the subtleties of the piano tone. The sound board isrestrained in its. vibratory motion because the edges are rigidlymounted to the frame. The conventional sound board is not an efficientradiator of sound.

The diaphragmatic mounting of the conventional structural sound boarddoes not provide the proper degree of stiffness throughout the length ofthe bridge. The stiffness at any particular point on the bridge isdependent upon the distance of the point from the edges of the soundboar-d. The treble region is quite stiff, the center register is lessstiff, but the bass register is more stiff due to its increasedproximity to the edge of the sound boa-rd. Unfortunately the bass notesshould be supported with the least degree of stiffness. The bass notesof a conventional piano are normally too stiffly supported.

Various means have been employed in an attempt to decrease theacoustical stiffness of the support for the bass strings. One means,that is employed on most pianos, is to overstring the bass register byusing a separate bass bridge that is mounted away from the edge of thesound board. The result is only partially satisfactory because theproper gradation of stiffness is not achieved.

This invention discloses a novel method of constructing a piano in whichmeans for radiating the sound and mean for providing the acousticalstiffness at the bridge are accomplished by two different members. Thesepara- 3,312,136 Patented Apr. 4, 1967 "ice tion of the sound radiatingmeans from the stiffness means allows the sound radiator to be designedas an efficient, responsive radiator of sound, and allows the acousticalstiffness at the bridge to be designed to be optimum for each string. Agreatly improved balance of sound radiating properties and a propergradation of stiffness are thus possible with this invention.

In this invention, the sound board is mounted to the frame along oneedge and is essentially vibrationally free along the other edges. Thesound board i mounted to theframe acoustically relatively tightly alongthe edge parallel to the hammer strike line and opposite to the bridge,and is acoustically relatively loosely coupled to the frame along thesides and edge adjacent to the bridge. This duo mounting method permitsthe sound board to vibrate in a generally pivotal manner in which theradiating surface vibrates pivotally about the tightly coupled edge. Theloose coupling of the sound board to the frame along the other edgespermit the sound board to vibrate generally freely and unrestrainedunder the driving action of the bridge.

The mounting of the sound board to the frame, or case, must be properlyaccomplished so that the sound board vibrates, at least in itsfundamental mode, in a generally angular manner. The sound board must berelatively tightly coupled to the frame along its mounted edge. Thesound board may be rigidly coupled in which case the tightly couplededge does not translate or rot-ate relative to the frame, and theangular vibrational motion i accomplished by the flexure of the soundboard itself in the vicinity of the mounted edge. The sound board may bepivotally coupled to the frame along its mounted edge, in which case thesound board does not translate but may rotate along its mounted edge.The sound board may be stifily coupled to the frame along its mountededge. The stiff support would allow the generally fined edge of thesound board to vibrate, both translatory and rotary, although suchvibration of the generally fixed edge would necessarily be small.

The sound board must be relatively loosely coupled to the frame alongits generally vibrationally free edge so that the sound board mayvibrate in a generally angular manner. The least possible couplingbetween the free edge of the sound board and the frame is a completeabsence of any physical connection; a freely suspended edge.

The loosely coupled edge of the sound radiator may be compliantlymounted to the frame. A compliant mount somewhat restrains the motion ofthe free edge of the sound board, but some degree of vibrational freedomis afforded.

The relative gradations of the tightness or looseness .of 'the couplingof the edge of the sound board to the frame are, in decreasing order oftightness: rigid, pivoted, stiff, compliant, and free. A rigid, pivoted,or stiff coupling are a relatively tight coupling, and a compliant, orfree coupling are a relatively loose coupling.

For the purpose of definition, a relatively tight coupling between theframe and the edge of the ound board is a coupling in which theamplitude of the vibration of the edge of the sound board is small incomparison to the amplitude of vibration of the bridge. A relativelyloose coupling between the frame and edge of the sound board is acoupling in which the amplitude of vibration of the edge of the soundboard is of the same order as the amplitude of vibration of the bridge.I

The degree of coupling that constitutes a tight coupling and the degreeof coupling that constitutes a loose coupling are dependent upon theacoustical para-meters of the string-sound board system. Thus a tightcoupling and a loose coupling of the edge of the sound board to theframe can be defined in terms of each other. A relatively tight couplingof the sound board to the frame together with a relatively loosecoupling of the sound board to the frame cooperate so as to support thesound board in such a manner that the sound board may vibrate under theaction of the strings, in a generally angular vibrational manner.

In this invention the acoustical stiffness at the bridge is provided bysprings that are disposed between the bridge and an extension of theframe that lies beneath the bridge. The spring constant of these springsis varied along the length of the bridge to provide the proper degree ofstiffness for each note.

The sound board in this invention can be made from a variety ofmaterials and can be constructed in a variety of modes. It can be madefrom wood, metal, plastic, foamed plastic, or paper. The sound radiator,for best results, should be designed so that it possess suflicientstrength to withstand the inertial and air loads.

A preferred embodiment of the invention is illustrated in theaccompanying drawings in which:

FIGURE 1 is a plan view of the piano frame-stringsound board systemshowing the layout of the frame, the strings, and the sound board.

FIGURE 2 is a sectional view along line 2--2 in FIG- URE 1 showing asound board that is rigidly mounted and freely suspended.

FIGURE 3 is a sectional view along line 2-2 in FIGURE 1 showing a soundboard that is pivotally mounted and compliantly suspended. I

FIGURE 4 is a sectional view along line 2--2 in FIG- URE 1 showing asound boardthat is stifily mounted and resiliently suspended.

FIGURE 5 is an enlarged detail section along line 22 in FIGURE 1 showingthe stiffness means.

- Referring to the drawings, FIGURE 1 show a frames tring-sound boardsystem constructed in accordance with the principles of this invention.A frame If such as might be used in a piano tensionally supports a fullcomplement of musical strings indicated in general by numeral 11. Thetail end of each of the strings is attached by means of a hitch pin 12to the hitch portion 13 of frame 10. The head end of each of the stringsis attached to frame by means of a tuning pin 14. p

The strings 11 vibrate between fixed bar 15, that is part of frame 10,-and vibrating bridge 16. Bridge 16 is secured with glue to sound board17. Sound board 17 is acoustically tightly coupled to frame 11] alongmounting edge 18, and is acoustically loosely coupled to frame 10 alongsuspended edges 19, 20, and 21. The sound board, by this duo mountingmethod, is free to vibrate in an angular manner in which it pivots alongmounting edge 18, and freely vibrates along the suspended edges 19, 2t),and 21.

The acoustical stiffness at bridge 16 is provided by the plurality ofsprings 22 that are disposed between the sound board 17 under bridge 16and a portion of the frame 23 that extends in spaced proximity to bridge16.

The springs 22 provide the acoustical stiffness with which bridge 16must be supported to produce a pleasing tone. The springs can be placedone under each string, under groups of strings, or a single pring membercould be extended along the entire length of the bridge.

FIGURE 2 shows one method of relatively tightly coupling sound board 17along edge 18 to frame 10 and one method of relatively loosely couplingthe sound board along edges 19, 2t and 21 to frame 10. The sound board17 is rigidly secured with glue to mounting projection 24 on frame 10.The gluing of the sound board directly to the frame forms a rigidcoupling that prevents the edge 13 of the sound board from vibrating orrotating relative to the frame.

The sound board 17 i freely suspended at 25 along edges 19, 20, and 21.The absence of physical contact between sound board 17 and frame 10provides the loosest possible acoustical coupling between the soundboard and the frame.

FIGURE 3 shows another method of relatively tight- 1y coupling' soundboard 17 along edge 18 to frame 16,

and another method of relatively loosely coupling the sound board alongedges 19, 20, and 21 to frame 10. The sound board 17 is pivotallysecured to frame 10 by means of fiexural pivot member 26. Flex-uralpivot member 26 is secured with glue to the edge 18 of sound board 17.Flexural pivot member 26 is secured with glue to projection 27 of frame10. The flexural member permits the sound board to pivot generally aboutedge 18, yet fully restrains its translatory vibratory movement in aplane normal to the strings.

The sound board 17 is relatively loosely coupled to frame 17 along theedges 19, 20, and 21 by mean of a compliant member 28. Compliant member28 is secured with glue to frame 10 and is secured with glue to soundboard 17. A compliant mount can also be fashioned by flexiblycorrugating the edges 19, 20, and 21 of the sound board. A compliantmount provides a relatively loose coupling between the sound board andthe .frame.

FIGURE 4 shows still another method of relatively tightly coupling soundboard 17 along edge 18 to frame 10, and a variation of a method ofrelatively loosely coupling the sound board along edges 19, 20, and 21to frame 10. Sound board 17 is relatively tightly coupled to frame 10 bymeans of stiff member 29. Stiff member 29 is secured with glue to edge18 of sound board 17, and is secured with glue to mounting projection24' on frame 10. Stiff member 29, because of its cantilever deflection,allows the edge 13 of sound board 17 to vibrate in a highly restrainedmanner.

The sound board 17 isrelatively loosely coupled to frame 17 along theedges 19, 2t), and 21 by means of a compliant member 30. Compliantmember 30 can be any elastic material such as soft rubber, foamedplastic, and the like. Compliant member 30 is securedwith glue to theedge of sound board 17 and is secured with glue to hitch pin support 13on frame 10. The compliant member may restrain the motion of edges 19,2t), and '21 of sound board 17, but still allow the sound board tovibrate in a somewhat angular manner.

FIGURE 5 is an enlarged detail of the springstiffncss means. String 11passes over bridge 16. The slight downward angle, or downbearin'g ofstring 11 after it passes over bridge 16, causes the string to betightly coupled to bridge 16 at bridge point 31. Bridge point 31 must beprovided with a proper degree of acoustical stiffness for the musicaltone to be pleasing. The acoustical stiffness at bridge point 31 isprovided by a stiff member 22 that is disposed between the sound board17 and the frame projection 23. The stiff member 22 is coupled to bridgepoint 31 through sound board 17 and bridge 16. The stiff member 22 isshown as a spring.

The foregoing disclosure has been described for a sound board, such asmight be used in a piano in which the means for radiating sound and themeans for providing acoustical stiffness are accomplished by separatemembers; and in which the sound board vibrates in an angular manner dueto mounting one edge of the sound board relatively tightly to the frame,and the other edges relatively loosely to the frame.

This invention has been disclosed as "being applicable to a piano, butit will be apparent to one skilled in the art that the invention is alsoapplicable to other stringed musical instruments.

It willherein be understood, of course, that these embodiments of theinvention have been used for illustrative purposes only and that variousmodificationsand variations in the present invention may be effectedwith out departing from the spirit and scope of the novel conceptsthereof.

I claim:

1. A stringed musical instrument comprisingz' a frame,

a plurality of strings tensionally supported by said frame,

bridge means coupled to said strings,

stiffening means coupled between said bridge means and said frame, and

sound radiator means coupled to said bridge means,

part of the periphery of said sound radiator means being acousticallyrelatively tightly coupled to said frame and part of the periphery ofsaid sound radiator means being acoustically relatively loosely coupledto said frame.

2. A stringed musical instrument comprising:

a frame, 1 1

a plurality of strings tensionally supported -'by said frame,

bridge means coupled to said strings,

stiffening means coupled between said bridge means and said frame, and

sound radiator means coupled to said bridge means,

said sound radiator means being acoustically relatively tightly coupledto said frame along the edge opposite from said bridge means, and beingacoustic-ally relatively loosely coupled to said frame along the edgeadjacent to said bridge means.

3. A stringed musical instrument in accordance with claim 2 wherein:

said sound radiator means is rigidly coupled to said frame along theedge opposite from said bridge means, and is compliantly coupled to saidframe along the edge adjacent to said bridge means.

4. A stringed musical instrument in accordance with claim 2 wherein:

said sound radiator means is rigidly coupled to said frame along theedge opposite from said bridge means, and is freely suspended along theedge adjaoent to said bridge means.

5. A stringed musical instrument in accordance with claim 2 wherein:

said sound radiator'means is pivotally coupled to said frame along theedge opposite from said bridge means, and is compliantly coupled to saidframe along the edge adjacent to said bridge means. -6. A stringedmusical instrument in accordance with claim 2 wherein:

said sound radiator means is pivotally coupled to said frame along theedge opposite from said bridge means, and is freely suspended along theedge adjacent to said bridge means. 7. A stringed musical instrument inaccordance with claim 2 wherein:

said sound radiator means is stifily coupled to said frame along theedge opposite from said bridge means, and is compliantly coupled to saidframe along the edge adjacent to said bridge means. 8. A stringedmusical instrument in accordance with claim 2 wherein:

said sound radiator means is stiflly coupled to said frame along theedge opposite from said bridge means, and is freely suspended along theedge adjacent to said bridge means.

RICHARD B. WILKINSON, Primary Examiner.

C. M. OVERBEY, Assistant Examiner.

1. A STRINGED MUSICAL INSTRUMENT COMPRISING: A FRAME, A PLURALITY OFSTRINGS TENSIONALLY SUPPORTED BY SAID FRAME, BRIDGE MEANS COUPLED TOSAID STRINGS, STIFFENING MEANS COUPLED BETWEEN SAID BRIDGE MEANS ANDSAID FRAME, AND SOUND RADIATOR MEANS COUPLED TO SAID BRIDGE MEANS, PARTOF THE PERIPHERY OF SAID SOUND RADIATOR MEANS BEING ACOUSTICALLYRELATIVELY TIGHTLY COUPLED TO SAID FRAME AND PART OF THE PERIPHERY OFSAID SOUND RADIATOR MEANS BEING ACOUSTICALLY RELATIVELY LOOSELY COUPLEDTO SAID FRAME.